Most of the plants we specify for our gardens are hardy enough to cope with British winters. We’re careful about that. But even hardy plants appreciate a helping hand when temperatures dip, and if you’ve added a few tender specimens to your borders, they’ll need attention before the cold arrives.
Understanding Frost Damage
Frost forms when temperatures drop below zero. The water inside plant cells freezes and expands, rupturing the cell walls – which is why frost-damaged plants look blackened, limp or translucent after a hard frost. Morning sun then makes things worse by causing rapid thawing.
Cold winds also dry out plant tissues, especially evergreens, while freeze-thaw cycles in soil can heave plants right out of the ground, exposing their roots. So it’s important we protect garden plants from frost.
Plants That Need Protection
Hardy stalwarts like lavender, clematis, hydrangeas and most roses can handle short freezing spells without fuss. Native plants generally look after themselves.
However, the plants needing help are tender perennials, such as salvias, fuchsias, and pelargoniums, as well as exotics like tree ferns, palms, citrus and olive trees. Dahlias, cannas and begonias sit in between – their roots will often survive if protected, but the first hard frost will blacken their top growth.
Mulching is Your First Line of Defence
Mulching is the most effective thing you can do. Apply a layer at least 5cm thick around vulnerable plants from late autumn. Use organic materials – bark chippings, straw, well-rotted manure or old leaves. The mulch insulates the soil and prevents damaging frost from getting into the ground.
Keep mulch a few centimetres away from plant stems to avoid rot, and don’t compress it. You want to keep air circulating whilst providing that protective blanket.
Other Protection Methods
Horticultural fleece is invaluable when frost threatens. Heavier grades can provide about 2°C of protection whilst allowing light, air and water through. Cover vulnerable plants overnight and remove during milder spells to prevent overheating.
Container plants are particularly at risk during cold spells because their roots have less insulation. Move pots to sheltered spots against walls or into unheated greenhouses. If they’re too heavy, wrap the containers in bubble wrap or hessian and raise them on pot feet or bricks. This improves drainage and helps prevents cracking.
For tender bulbs and tubers, you have choices. Dahlias can be lifted after the first frost has blackened their foliage. Dry them upside down in a frost-free place, then store in boxes covered with sand or compost until spring. Or leave them in the ground under thick, dry straw mulch. Cannas, pelargoniums and fuchsias can be cut back and kept barely damp in a shed or garage over winter.
Dealing with Snow
Snow can be helpful or harmful depending on the type that falls. A layer of powder snow can act as an insulator once it reaches about 5cm thick. But heavy, wet snow can snap branches, flatten shrubs and damage hedges.
When snow settles, gently brush it off trees, shrubs and hedges before it builds up. Don’t shake branches vigorously – frozen wood becomes brittle. If you live in an area prone to heavy snow, make sure to taper the tops of hedges during the summer pruning season so snow does not sit heavily on top, but slides down the sides.
Clear snow from greenhouses and polytunnels before the weight causes damage. And avoid walking on snow-covered lawns – you’ll compact and damage the turf.
Getting the Timing Right
It’s best to set up protection before the cold weather arrives rather than scrambling around when frost is predicted. Get stakes or supports in place at least a week ahead – frozen ground makes this nearly impossible. Keep your eye on the forecasts and be ready.
One thing to avoid: don’t feed plants with nitrogen-rich fertiliser from late summer onwards. They encourage soft growth that’s particularly vulnerable to frost.
The good news is that most plants are tougher than you think. But with a bit of preparation, your garden will come through winter ready for spring.